1. Field of the Invention
The present invention relates to an illuminating device, a light guide body and a liquid crystal display device.
2. Description of the Related Art
The illuminating device such as a front light, a back light, etc. used in the liquid crystal display device, etc. is basically constructed by a light guide plate and a light source arranged on its side end face. An illuminated body such as a liquid crystal panel, etc. is illuminated by reflecting light introduced from the side end face of the light guide plate by a prism shape formed on the face on the side opposed to the emitting face of the light guide plate and emitting this light from the emitting face (for example, see patent literature 1).
FIGS. 6A and 6B are views showing a sectional structure of the liquid crystal display device having each of these conventional illuminating devices, etc. FIG. 7 is an explanatory view for explaining a light guide state of the front light shown in FIG. 6A. FIG. 8 is an explanatory view for explaining a light guide state of the back light shown in FIG. 6B.
The liquid crystal display device shown in FIG. 6A is constructed by a liquid crystal panel 120 and a front light 110 arranged on its front face side (upper face side in this figure). In the front light 110, reference numerals 112, 113 and 115 respectively designate a light guide plate, a bar light guide body and an LED (light emitting diode). A projecting stripe 114 of a triangular shape in section constructed by a gentle slanting face portion 114a and a steep slanting face portion 114b is continuously formed on the upper face of the light guide plate 112. In the liquid crystal panel 120, reference numerals 121, 122, 123 and 124 respectively designate an upper substrate, a lower substrate, a liquid crystal layer and a sealant. An unillustrated reflection plate is arranged on the outer or inner face side of the lower substrate 122 in the liquid crystal panel 120.
The liquid crystal display device shown in FIG. 6B is constructed by a liquid crystal panel 140 and a back light 130 arranged on its rear face side (lower face side in this FIG.). The liquid crystal panel 140 is set to a transmission type having no reflection layer, or a semi-transmission reflection type in which-the reflection layer is partially arranged. The other basic constructions are similar to those of FIG. 6A. In the back light 130, reference numerals 132 and 133 respectively designate a light guide plate and a light source (for example, a cold cathode tube). Plural grooves 134 of a wedge shape in section are formed on the lower face of the light guide plate 132.
[Patent Literature 1]
Japanese Unexamined Published. Patent Application No. H11-109347
In the front light 110 shown in FIG. 6A, as shown in FIG. 7, light introduced from the bar light guide body 113 into the light guide plate 112 is propagated while this light is repeatedly totally reflected within the light guide plate 112. The light incident two the steep slanting face portion 114b is mainly emitted from the emitting face 112b of the light guide plate 112 (lights A, B shown in FIG. 7). However, with respect to the light incident to the steep slanting face portion 114b similarly to the lights A, B, as shown by lights C, D shown in FIG. 7, there is a case in which light incident to the slanting face portion at an incident angle shallower than that of each of the lights A, B is transmitted through the steep slanting face portion 114b and is leaked out to the upper face side of the liquid crystal display device. This is because the incident angles of the lights C, D become shallow over a critical angle in the light guide plate 112 and the air. Since such lights C, D are not utilized as illumination light, these lights C, D reduce brightness of the front light 110 and become a cause reducing contrast with respect to the display in which these lights are transmitted through the light guide plate 112.
Further, in the liquid crystal display device shown in FIG. 6B, as shown in FIG. 8, one portion of light propagated within the light guide plate 132 is incident to the lower face 132b of the light guide plate 132 at a shallow incident angle over the critical angle, and is transmitted outward from the lower face 132b so that this light portion is lost. Further, the shape of the back light 130 shown in FIG. 6B is a shape generally used at present. However, in the back light of this kind, the light emitted from the light guide plate 132 to the liquid crystal panel 140 side includes many components shifted from the direction perpendicular to the light guide plate 132 and slantingly emitted. Therefore, a problem exists in that the utilization efficiency of light after the emission from the back light 130 is reduced. A prism sheet 137 for directing the emitted light of the back light 130 to the direction perpendicular to the light guide plate was arranged between the light guide plate 132 and the liquid crystal panel 140 to solve this problem. However, in this construction, it is difficult to make the liquid crystal display device thin and the problem,of an increase in cost is caused.